Water flow switches for sprinkler operation indication have been available for decades. Over the years a single design has evolved which consists of a switch body, a snap-action switch, a plunger which extends into the sprinkler riser and a paddle assembly which is connected to the switch body via a pivot. The paddle partially obstructs the cross-section of the pipe. When water begins to flow the paddle swings down-stream, rotating about the pivot. A cam on the paddle depresses (or releases, depending upon the design) the plunger which transmits the motive force of the paddle into the switch interior. The movement of the plunger actuates, either immediately or through a mechanical time delay called a "retard", the snap-action electro-mechanical switch, providing an electrical signal to the fire alarm control panel.
There have been a number of persistent problems with this design. The plunger must be sealed with either rubber boots or o-ring seals to prevent the leakage of water from the sprinkler pipe interior into the switch interior. This need for a sealing force results in the need for relatively large mechanical forces on the paddle. However, large required forces on the paddle result in the need for commensurately large hydraulic forces due to water flow. These large forces necessitate large water flows before the reliable actuation of the switch can be achieved. In addition, the occasional oscillation of water within the sprinkler system due to pressure fluctuation in the public utility water mains necessitates a "retard" feature. This requires the introduction of a time delay between the operation of the sensing paddle and the actuation of the electro-mechanical switch. The current state of the art relies on mechanical time delays to implement the "retard" feature. This adds to the complexity and cost of the flow switch as well as reducing its inherent reliability.
It is also desirable to provide a capability to measure a particular flow rate of the fluid in the conduit. The use of inherently reliable solid state circuitry to accomplish this is a further contribution of this invention.
In 1996 this inventor developed an Electro-Optical Valve Status Supervision Switch. U.S. Pat. No. 5,584,319 was issued on Dec. 17, 1996 for this invention. This invention utilized a reflective pit on the stem of an outside screw and yoke valve situated opposite an LED/phototransistor pair to monitor when the valve was not fully open. This development is helpful in implementing the objectives of this invention.
It is therefore a primary object of this invention to provide a fluid flow detection device having a passive interface between the signal sensing portion and the signal generation portion and the flow responsive element wherein the signal generation and sensing portions employ reliable, solid state electronic circuitry.
It is a further object of this invention that the detection device include reliable electronic circuitry to distinguish between fluid flows that are of sufficient amount and are continuous for at least a certain minimum amount of time.
It is still a further object of this invention is to employ the fluid flow detection device of this invention to detect water flows in fire protection sprinkler systems.
It is yet another object of this invention to employ certain elements of a flow responsive element presently used in the art, but which is adapted to accommodate the signal generation and sensing functions of the present invention.
A still further object of this invention is to provide a fluid flow detection device which can sense and indicate specific fluid flow rates.